Ground drive apparatus for progressive cavity pumps

ABSTRACT

A ground drive apparatus for a progressive cavity pump in which a rotor of the pump is connected to a rod string and in which the rod string is connected to the polished rod. The ground drive apparatus has a motor with a hollow shaft, an upper sealing structure positioned above the motor and extending around the polished rod, and a well sealing structure positioned below the motor so as to the selectively in sealing and clamping relationship with the polished rod. The hollow shaft has an inner diameter greater than an outer diameter of the rotor and the rod string. The upper sealing structure includes a stationary sealing cap, a rotary sealing bushing extending around the stationary sealing cap, and a sealing ring interposed between the stationary sealing cap and the rotary sealing bushing. The well sealing structure has a housing with a piston slidably mounted in the housing.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

INCORPORATION-BY-REFERENCE OF MATERIALS SUBMITTED ON A COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to progressive cavity pumps. More particular, the present invention relates to the direct drive of such progressive cavity pumps as used in oil and gas operations. More particularly, the present invention relates to a ground drive apparatus for a progressive cavity pump which is cooperative with the polish rod for the driving of the pump.

2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.

A progressive cavity pump is a type of positive displacement pump. The progressive cavity pump transfers fluid by means of the progress, through the pump, of a sequence of small, fixed shape, discrete cavities, as its rotor is turned. This leads to the volumetric flow rate being proportional to the rotation rate and to low levels of shearing being applied to the pump fluid. These pumps have application in fluid metering and the pumping of viscous or shear-sensitive materials. The cavities taper down toward their ends and overlap with their neighbors, so that, in general, no flow pulsing is caused by the arrival of cavities at the outlet, other than that caused by compression of the fluid or pump components.

The progressive cavity pump includes a helical rotor and a twin helix, twice the wavelength and double the diameter of the stator. The rotor seals tightly against the stator as it rotates, forming a set of fixed-sized cavities in between. The cavities move when the rotor is rotated that their shape or volume does not change. The pump material is moved inside the cavities.

Specific designs of progressive cavity pumps involve the rotor of the pump being made of a steel material, coated with a smooth a hard surface, normally chromium, with the body (i.e. the stator) formed of a molded elastomer inside a metal tube body. The elastomer core of the stator forms the required complex cavities. The rotor is held against the inside surface of the stator by angled link arms, bearings (immersed in the fluid) allowing it to roll around the inner surface.

In the past, a variety of mechanisms have been utilized for the driving of such progressive cavity pumps. Typically, in the past, a motor has been located to the side of the pump and connected to the polished rod of the pump through a series of gears, chains, sprockets, and similar mechanisms. Typically, an asynchronous motor is connected to the polished rod through a belt transmission to a drive gearbox. The gearbox then drives the polished rod of the screw pump in order to achieve the rotary motion. These types of systems have various problems. First, the transmitted power is limited. The belt can easily slip and become damaged. The teeth of the gearbox are easily broken and damaged. As such, the high torque requirements are not able to be achieved.

These prior drive systems also require a large amount of mechanical maintenance. As a result, a high operation cost is necessary. Rotary sealing components must be installed within the gearbox. Also, the reliability of the belt transmission is rather poor. This can lead to a large amount of mechanical maintenance and high operating costs during the operation of such drive systems.

The efficiency of such drive systems is very low. In order to effectively start the progressive cavity pump, the motor will often have to have up to three times the power required for starting than during normal operation. As a result, the motor will need to be oversized in order to achieve the starting requirements. This can lead to further inefficiency. Additional problems include the need to adjust the capacity, the belts, or the operational parameters of the drive system during the various pumping stages. The noise of such systems is rather loud. Additionally, the area required for such a drive equipment is rather large. As such, it will occupy rather large footprint within the oil extracting area.

Recently, developments have led to the use of direct drive motors in association with such progressive cavity pumps. One example of a low-speed direct drive apparatus for a progressive cavity pump was disclosed in Chinese Patent Publication No. CN 1683791. This patent publication describes a screw pump device that has a polished rod, a shaft coupling, a low-speed motor, a motor controller, a fixing seat, and a screw pump. The motor shaft of the low-speed motor is hollow and positioned within the polished rod. The motor shaft is fixed to the polished rod using a shaft coupling. The polished rod passes through the central hole of the fixed seat and connects to the shaft of the screw pump downhole. The low-speed motor is fixed onto the fixed seat. The motor controllers are installed within the terminal box of the low-speed motor. A matching controller for the low-speed motor is employed. The motor directly drives the screw pump and does not use a belt transmission for a speed change gear device. Since the motor shaft is connected to the pump shaft of the screw pump through the polished rod, the reactive power loss is decreased, the system efficiency and reliability of the screw pump is increased, the oil extracting cost is reduced, and the volume and weight of the screw pump is reduced.

U.S. Pat. No. 8,702,400, issued on Apr. 22, 2014 to Liu et al., teaches a surface motor direct-drive sucker-rod screw pump device. This screw pump devices is driven by a vertical three-phase permanent magnet brushless DC motor. The motor includes a motor controller, a rectifying circuit, and inversion circuit, a CPU and a driving circuit. The motor controller is used to adjust the voltage and frequency of the motor by the rectifying circuit, the inversion circuit, the CPU and the driving circuit. The speed of the motor can vary from zero to the maximum.

There have been difficulties with the prior art direct drive progressive cavity pumps. For example, when it is required to remove the rotor of a progressive cavity pump out of the well, the ground driving device has to be first removed in its entirety. Leaks can happen when using packing sealing. As such, more infilling would be required. Since the packing sealing is located at the bottom of the direct drive motor, it is difficult to access and replace. Any mechanical sealing is achieved by a pair of alloy surfaces and a spring. They are often damaged due to abrasion and corrosion when sand enters the area. Such sand is always contained in crude oil. As such, damage to the mechanical sealing can often occur. The mechanical sealing requires strict dimensional control on the parts. As such, it is not easy to assemble and maintain. The mechanical sealing of these prior art devices can only withstand 2 MPa of pressure. The existing well sealing devices either seal the well or clamp the polished rod, but not both.

It is an object of the present invention to provide a ground drive apparatus for a progressive cavity pump which facilitates the ability to repair the rotor of the pump without the need to remove the ground drive apparatus.

It is another object of the present invention to provide a ground drive apparatus for a progressive cavity pump which enhances the sealing capability.

It is still a further object of the present invention to provide a ground drive apparatus for a progressive cavity pump that maintains the pressure of the well and also has the ability to clamp the polished rod tightly.

It is still a further object of the present invention to provide a ground drive apparatus for a progressive cavity pump which facilitates the ability to maintain the ground drive apparatus.

It is still a further object of the present invention to provide a ground drive apparatus that maximizes the pressure-retaining capability.

It is another object the present invention to provide a ground drive apparatus for a progressive cavity pump that can both seal the well and clamp the polished rod.

It is still a further object of the present invention to provide a ground drive apparatus for a progressive cavity pump which minimizes damage to mechanical sealing due to abrasion and corrosion.

These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.

BRIEF SUMMARY OF THE INVENTION

The present invention is a ground drive apparatus for a progressive cavity pump in which the pump has a rotor affixed to a rod string of a production well thereon. The rod string has a polished rod at the ground drive apparatus. The ground drive apparatus includes a motor having a hollow shaft, an upper sealing structure positioned above the motor and suitable for extending around the polished rod, and a well sealing structure positioned below the motor so as to be selectively in sealing relation with the polished rod. The motor has a hollow shaft. The polished rod will extend through an interior of the hollow shaft. The hollow shaft has an inner diameter greater than the outer diameter of the rotor and/or an outer diameter of the rod string.

The upper sealing structure is in sealing relationship with the hollow shaft such that the sealing provents any downhole fluid from leaking into the motor. The upper sealing structure includes a stationary sealing cap, a rotary sealing bushing extending around the stationary sealing cap, and a first sealing ring interposed between the stationary sealing cap and the rotary sealing bushing. A second sealing ring is interposed between the lower end of the rotary sealing bushing and the hollow shaft. The lower end of the rotary sealing ring extends downwardly below a lower end of the stationary sealing cap. The first sealing ring has a V-shaped cross-section. The rotary sealing bushing is cooperative with the motor so as to rotate in relation to the rotation of the rod by the motor. The first sealing ring includes a plurality of sealing rings positioned in spaced relation to each other and extending around the stationary sealing. A rod clamp holds/grasps the polished rod by clamping so as to cause the rod to be rotated with the motor. The rod clamps also hold the axial load of the rod string.

The well sealing structure includes a housing positioned around the polish rod, and a piston slidably mounted in the housing. The piston is slidable in a radial direction toward or away from the polish rod. The piston has teeth formed thereon or affixed thereto at an end facing the rod. A sealing element is fixed to the end of the piston. The sealing element extends so as to be in sealing relation with the polish rod when the piston is moved such that the teeth are engaged with the polish rod. A tightening screw is engaged with the piston and extends outwardly therefrom. The tightening screw is actuatable so as to move the piston toward or away from the polish rod. A nut is received by the housing. The tightening screw is threadedly received by the nut. The end of the piston extends substantially around an outer diameter of the polish rod.

This foregoing Section is intended to describe, with particularity, the preferred embodiment of the present invention. It is understood that modifications to this preferred embodiment can be made within the scope of the present invention without departing from the true spirit of the invention. As such, this Section should not to be construed, in any way, as limiting of the broad scope of the present invention. The present invention should only be limited by the following claims and their legal equivalents.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a side elevational view showing the ground drive apparatus for a progressive cavity pump in accordance with the preferred embodiment the present invention.

In FIG. 2 is a cross-sectional view showing a traditional prior art packing sealing.

FIG. 3 is a cross-sectional view showing traditional prior art mechanical sealing.

FIG. 4 is a cross-sectional view showing the upper sealing structure of the present invention.

FIG. 5 is a cross-sectional view showing the well sealing structure of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is shown the ground drive apparatus 10 in accordance with the preferred embodiment of the present invention. A polished rod 12 is shown extending through the ground drive apparatus 10 in a generally vertical orientation. Rod clamps 14 engage the polished rod 12 and are interconnected to the motor 16 such that a rotation of the motor 16 can cause a corresponding rotation of the polished rod 12. The upper sealing structure 18 is positioned at the top of the motor 16 and below the rod clamps 14. The upper sealing structure 18 is illustrated, with particularity, in FIG. 4 herein. The motor 16 has the well sealing structure 20 at the lower end thereof. In FIG. 1, it can be seen that an oil outlet 22 is provided below the well sealing structure 20 so as to allow for the discharge of oil, and other fluids, from the well. A wellhead flange 24 is positioned at the bottom of the ground drive apparatus 10 such that the apparatus 10 can be secured to the wellhead. The polished rod 12 is illustrated as extending downwardly so as to be received within the well. The polished rod 12 will connect with a downhole rod string extending downwardly therefrom. A well pump will be connected to the rod string in a conventional manner. The progressive cavity pump will include a suitable rotor that has a particular outer diameter.

FIG. 2 illustrates a prior art packing sealing 30 that has been utilized in direct association with the polished rod 32. As can be seen in FIG. 2, the polished rod 32 extends through the interior of the packing seals 34 located within the body 36 of the packing seal 30. The packing seals 34 are received within a channel formed within the body 30 and extends around the polished rod 32 such that the packing seals 34 are in direct contact with the exterior surface of the polished rod 32. A compression cap 38 is fitted over the opening at the top of the body 34 and inserted thereinto so as to effectively compress the packing seals 34 so that the are in close contact with the exterior surface of the polished rod 32.

As can be seen in FIG. 2, it is necessary to remove the rotor from the well, then the entire structure of the ground drive apparatus would have to be removed. There is no space available whereby the rotor can pass through the interior of the body 32 through which the polished rod 32 extends. As such, a great deal of effort will be required so as to effectively remove the ground drive apparatus such that the rotor can be removed. Additionally, in FIG. 2, it should be noted that the packing sealing 34 can allow for leaks. The packing sealing 34 lacks effective infilling. Typically, the traditional packing sealing 30 would be located at the bottom of the ground drive apparatus. As such, it would be difficult to access and replace, if required.

FIG. 3 shows a traditional mechanical sealing 40 as used in the prior art. It can be seen that the mechanical sealing 40 includes a pair of alloy surfaces 42 and 44. A spring 46 will extend between these alloy surfaces. The polished rod 48 and extends through the interior of the pair of alloy surfaces 42 and 44. The mechanical sealing 40, as shown in FIG. 3, can often become damaged due to abrasion and corrosion caused by contact with the pump fluids. As such, frequent repair and replacement would be required. The mechanical sealing assembly 40 requires strict dimensional control of the various components thereof. As such, it is very difficult to assemble and maintain. This mechanical sealing assembly 40, when in use, can only withstand up to 2 MPa of pressure. As such, it has not been particularly effective for use on a ground drive apparatus for the direct drive of a progressive cavity pump.

FIG. 4 illustrates the upper sealing structure 18 as used in the present invention. The upper sealing structure 18, as can be seen in FIG. 1, is actually positioned above the motor 16 and extends around the polished rod 12. Importantly, in FIG. 4, it can be seen that there is a hollow shaft 50 that is positioned on the interior of the upper sealing structure 18. The hollow shaft 50 will extend through the motor and extend to the well sealing structure 20. The hollow shaft 50 has an inner diameter that is greater than the outer diameter of the rotor of the progressive cavity pump and also greater than the rod string. Additionally, it can be seen that the polished rod 12 has an outer diameter that is less than the inner diameter of the hollow shaft 50. The upper sealing structure 18 is illustrated as in sealing relationship with the hollow shaft 50. The upper sealing structure includes a stationary sealing cap 52, a rotary sealing bushing 54, and a first sealing ring 56. The rotary sealing bushing 54 will extend around the rotary sealing cap 52. The first sealing ring 56 is formed of a rubber material that is interposed between the stationary sealing cap 52 and the rotary sealing housing 54. The stationary sealing cap 52 is threadedly engaged with an external cylindrical surface of the hollow shaft 50. The first sealing ring 56 has a generally V-shaped cross-section, as can be seen in FIG. 4. A second sealing ring 58 is interposed between a lower end 60 of the rotary sealing bushing 54 and the hollow shaft 50. The second sealing ring 58 can be formed of a reinforced rubber material. As such, the second sealing ring 58 can bear against the outer surface of the hollow shaft 50.

The first sealing ring 56 includes a plurality of sealing rings 62 and 64 that are positioned in spaced relationship to each other and which extend around the stationary sealing cap 52. The lower end 60 of the rotary sealing bushing 54 extends downwardly below a lower end 66 of the stationary sealing 52. The rotary sealing bushing 54 is cooperative with the motor 16 so as to rotate in relation to the rotation of the polished rod 12 caused by the motor 16. As stated hereinbefore, the rod clamps 14 are connected to the polished rod 12 so as to cause the polished rod 12 to be rotated by the motor 16.

Since the upper sealing structure 18 is located at the top of the motor 16, this upper sealing structure 18 is easy to assemble and maintain. Suitable thrust bearings can be provided in the oil tank to withstand the axial load of the rod string. The multiple seals provided in the upper sealing structure 18 serve to avoid the possibility of leaks that often occurred using packing sealing. Since the hollow shaft 50 is larger than the outer diameter of the rotor of the progressive cavity pump, the disassembly of the rod clamps allows the rotor to be easily lifted through the interior of the motor 16 and the associated components.

FIG. 4 shows the well sealing structure 20 as used in the present invention. The well sealing structure 20 includes a housing 70 and a piston 74 slidably mounted within the housing 70. The piston 74 is slidable in a radial direction toward or away from the polished rod 12. The piston 74 can have teeth 76 formed thereon or affixed thereto at the end of the piston 74 facing the polished rod 12. A sealing element 78 is affixed to the end of the piston 74. The sealing element 78 extends so as to be in sealing relationship with the polished rod 12 when the piston 74 is moved such that the teeth 76 are engaged with the polished rod 12. A tightening screw 80 is engaged with the piston 74 and extends outwardly therefrom. This tightening screw 80 is actuatable so as to move the piston 74 toward or away from the polished rod 12. A holding nut 82 is positioned at an end of the housing 70. The tightening screw 80 is threadedly engaged with the holding nut 82. As such, a rotation of the tightening screw 80 with respect to the holding nut 82 will cause the tightening screw 80 translatably move of the piston 74.

In FIG. 5, it can be seen that when it is desired to grasp the polished rod 12, the tightening screw 80 can be rotated so as to move the piston 74 such that the teeth 76 will grip the exterior surface of the polished rod 12. Additionally, the sealing element 78 will bear against the outer surface of the polished rod 12 so as to create a seal therewith. This well sealing structure 20 not only keeps in the pressure of the well but also clamps the polished rod 12 very tightly. As such, this provides a significant degree of convenience for regular on-site maintenance Since the tightening screw 80 extends outwardly of the housing 70, it can be easily accessed at the bottom of the motor 16.

In FIG. 5, there is another piston 84 that is located on an opposite side of the polished rod 12. The piston 74 and the piston 84 can have a semicircular configuration. As such, when they art directed toward the polished rod 72 and engage therewith, they will entirely encircle the polished rod 12. Similarly, the sealing element 78 associated with the piston 84 will also encircle the polished rod 12 so as to provide a pressure-retention seal thereagainst. Another tightening screw 86 can extend outwardly of the housing 70 so as to actuate and cause the movement of the piston 84, in the manner described herein previously.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated construction can be made within the scope of the appended claims without departing from the true spirit of the invention. The present invention should only be limited by the following claims and their legal equivalents. 

I claim:
 1. A ground drive apparatus for a progressive cavity pump in which a polished rod is connected to a rod string, the rod string is connected to a pump rotor, the ground drive apparatus comprising: a motor having a hollow shaft, said hollow shaft having an inner diameter greater than an outer diameter of the pump rotor and an outer diameter of the rod string, said motor suitable for coupling to the polished rod so as to cause a rotation of said rod string; an upper sealing structure positioned above said motor suitable for extending around the polished rod; and a well sealing structure positioned below said motor so as to be selectively in clamping and sealing relationship with the polished rod.
 2. The ground drive apparatus of claim 1, said upper sealing structure being in sealing relation with said hollow shaft.
 3. The ground drive apparatus of claim 1, said upper sealing structure comprising: a stationary sealing cap threadedly engaged with said hollow shaft; a rotary sealing bushing extending around said stationary sealing cap; and a first sealing ring interposed between said stationary sealing cap and said rotary sealing bushing.
 4. The ground drive apparatus of claim 3, further comprising: a second sealing ring interposed between a lower end of said rotary sealing bushing and said hollow shaft.
 5. The ground drive apparatus of claim 3, said first sealing ring comprising a plurality of sealing rings positioned in spaced relation to each other and extending around said stationary sealing cap.
 6. The ground drive apparatus of claim 4, said lower end of said rotary sealing ring extending downwardly below a lower end of said stationary sealing cap.
 7. The ground drive apparatus of claim 3, said first sealing ring having a V-shaped cross-section.
 8. The ground drive apparatus of claim 3, said rotary sealing bushing cooperative with said motor so as to rotate in relation to the rotation of the polished rod by said motor.
 9. The ground drive apparatus of claim 1, further comprising: a rod clamp suitable for connection to the polished rod and to said motor so as to cause the polished rod to be rotated by said motor and to hold an axial load the rod string.
 10. The ground drive apparatus of claim 1, said well sealing structure comprising: a housing suitable for positioning around the polished rod; and a piston slidably mounted in said housing, said piston slidable in a radial direction toward or away from the polished rod, said piston having teeth formed thereon or affixed thereto at an end facing the polished rod.
 11. The ground drive apparatus of claim 10, further comprising: a sealing element affixed to said end of said piston, said sealing element extending so as to be in sealing relation with the polished rod when said piston is moved such that said teeth are engaged with the polished rod.
 12. The ground drive apparatus of claim 10, further comprising: a tightening screw engaged with said piston and extending outwardly therefrom, said tightening screw suitable actuatable as to move said piston toward or away from the polished rod.
 13. The ground drive apparatus of claim 12, further comprising: a nut received by said frame, said tightening screw threadedly received by said nut.
 14. The ground drive apparatus of claim 10, said end of said piston suitable for extending around an outer diameter of the polished rod.
 15. A ground drive apparatus for a progressive cavity pump in which the pump has a rotor thereon, the rotor being connected to a rod string, the rod string having a polished rod connected thereto, the ground drive apparatus comprising: a motor having a shaft, said motor suitable for connection to the polished rod so as to cause a rotation of the rod string; an upper sealing structure positioned above said motor and positioned so as to to be extendable around the polished rod, said upper sealing structure comprising: a stationary sealing cap; a rotary sealing bushing extending around said stationary sealing cap; and a first sealing ring interposed between said stationary sealing cap and said rotary sealing bushing; and a well sealing structure positioned below said motor so as to be selectively in sealing and clamping relation with the polished rod.
 16. The ground drive apparatus of claim 15, further comprising: a second sealing ring interposed between the lower end of said rotary sealing bushing and said hollow shaft, said lower end of said rotary sealing ring extending downwardly below a lower end of said stationary sealing cap.
 17. The ground drive apparatus of claim 15, said shaft being a hollow shaft, said hollow shaft having an inner diameter greater than an outer diameter of said rotor and an outer diameter of the rod string.
 18. A ground drive apparatus for a progressive cavity pump in which the pump has a rotor thereon, the rotor being connected to a rod string, the rod string having a polished rod connected thereto, the ground drive apparatus comprising: a motor having a shaft, said motor suitable for connection to the polished rod so as to cause rotation of the rod string; an upper sealing structure positioned above said motor and suitable for extending around the polished rod; and a well sealing structure positioned below said motor so as to be selectively in sealing and clamping relationship with the polished rod, said well sealing structure comprising: a housing suitable for positioning around the polished rod; and a piston translatably mounted in said housing, said piston suitable for translation in a radial direction toward or away from the polished rod, said piston having teeth formed thereon or affixed thereto at an end, said teeth surface for engaging the polished rod.
 19. The well sealing structure of claim 18, further comprising: a sealing element affixed to said end of said piston, said sealing element extending so as to be in sealing relation with the polished rod when said piston is moved such that said teeth are engaged with the polished rod.
 20. The ground drive apparatus of claim 18, said shaft being hollow, said shaft having an inner diameter greater than an outer diameter of the rotor and an outer diameter of the rod string. 